Biodegradable films have attracted attention as a means for facilitating waste processing of plastic films, and a variety of biodegradable films have been developed. Biodegradable films are subjected to hydrolysis or biodegradation in soil or water, the films are gradually destructed or decomposed, and eventually they are converted by action of microorganisms into nonhazardous decomposition products. Films molded from aromatic polyester resins, aliphatic polyester resins such as polylactic acid and polybutylene succinate, polyvinyl alcohol, acetate cellulose, starch, and the like are known as such films.
Because biaxially stretched films comprising polylactic acid, which is a biodegradable resin, excel in transparency, they started finding application as films for packaging, but such films have poor heat resistance.
A large number of methods comprising blending poly-L-lactic acid (PLLA) with poly-D-lactic acid (PDLA) and forming a stereocomplex have been suggested (for example, Japanese Patent Application Laid-open No. H9-25400 and Japanese Patent Application Laid-open 2000-17164; and Macromolecules, 20, 904 (1987)).
However, even when a composition obtained by simple melt kneading of PLLA and PDLA is molded into a film, a stereocomplex is not easily formed and although the film formed is improved in heat resistance, the film is brittle and difficult to use as a film for packaging or the like.